Previously, there is known a fuel injection valve that opens and closes an injection hole of a housing through reciprocation of a needle to inject fuel from an inside of the housing to an outside of the housing. For example, the patent literature 1 discloses a fuel injection valve that is configured such that an outer wall of a seal portion of a needle, which is contactable against a valve seat formed around an injection hole, is shaped into a form of a spherical surface that has a center in an inside of the needle.
When the seal portion is worn through repeated contact between the seal portion and the valve seat in the fuel injection valve, a fuel injection quantity of the fuel injection valve changes depending on a degree of wearing of the seal portion. In order to reduce the wearing of the seal portion, it is desirable to reduce a value known as a contact pressure that is obtained by dividing an application force, which is applied to the seal portion at the time of contacting the seal portion against the valve seat, by a cross sectional area of the seal portion, which is measured in a direction perpendicular to an application direction of the application force. Therefore, in general, the seal portion is formed to increase the above-described cross sectional area. In this way, even when the same application force is applied, the contact pressure is reduced. Thus, it is possible to reduce the wearing of the seal portion.
In the fuel injection valve of the patent literature 1, the outer wall of the seal portion is shaped into the form of the spherical surface, which has the center in the inside of the needle. Therefore, the cross sectional area, which is measured in the direction perpendicular to the application direction of the application force at the seal portion, is increased. However, due to resilient deformation of the seal portion, the location of the seal portion will deviate. Therefore, every time fuel is injected, the seat diameter may possibly change. Thus, the fuel injection quantity changes.
Furthermore, in the case where the outer wall of the seal portion is shaped into the form of the spherical surface, there may be a possibility of that a foreign object is continuously captured between the outer wall of the seal portion and the valve seat and thereby cannot be removed. Thus, it is difficult to ensure the fluid tightness in the valve closing time of the fuel injection valve.
In view of the above point, as a seal portion, which stabilizes a seat diameter to limit a change in the fuel injection quantity, there is proposed a seal portion that has tapered walls, which have different tapered angles. This seal portion is formed such that a boundary, which is formed between the tapered walls respectively having the different tapered angles, contacts the valve seat. Therefore, while the seat diameter is stabilized, a foreign object, which enters a gap between the outer wall of the seal portion and the valve seat, is crashed by the boundary to allow removal of the foreign object. However, in this seal portion, when an angle difference between the outer wall of the seal portion, which is located on the downstream side of the boundary, and the inner wall of the housing, which forms the valve seat, is increased in order to have a sufficient flow quantity of the fuel on the downstream side of the boundary, the contact pressure around the boundary of the seal portion is increased to possibly promote the wearing of the seal portion. In contrast, when the angle difference between the outer wall of the seal portion, which is located on the downstream side of the boundary, and the inner wall of the housing, which forms the valve seat, is decreased in order to reduce the contact pressure around the boundary of the seal portion, the sufficient flow quantity of the fuel, which is equal to or larger than a predetermined flow quantity, cannot be ensured on the downstream side of the boundary. Therefore, the required quantity of fuel, which is required for the injection, cannot be supplied to the injection hole.